Method for extruding gelatinous material

ABSTRACT

AQUEOUS POLYMER SOLUTIONS USEFUL AS FLOODING AGENTS IN THE RECOVERY OF PETROLEUM BY WATER FLOODING, AND IS ESPECIALLY ADAPTED FOR INSTALLATION AT THE SITE OF A WATER INJECTION WELL.   A METHOD FOR PROCUCING PARTICULATED GELATINOUS SUBSTANCES, SUCH AS GELATINOUS POLYMERS, AND SOLUTIONS OF THESE MATERIALS IN WHICH THE GEL IS FORMED IN A REACTION CHAMBER EQUIPPED WITH A HYDRAULICALLY ACTUATED PISTON THE PERFORATE EXTRUSION HEAD AND THE GELATINOUS PROCUCT IS SUBSEQUENTLY EXTRUDED INTO A STREAM OF SOLVENT OR NONSOLVENT LIQUID FLOWING AT RELATIVELY HIGH VELOCITY ON THE EXTERIOR OF THE PERFORATE HEAD. THE GELATINOUS SUBSTANCE IS DISPLACED FROM THE REACTION CHAMBER BY INTRODUCING A FLUID INTO THE REACTION CHAMBER ABOVE THE PISTON AT A SUFFCIENTLY ELEVATED PRESSURE TO DISPLACE THE SUBSTANCE FROM THE CHAMBER THROUGH THE PERFORATE EXTRUSION HEAD. THE HYDRAULIC PRESSURE ACTUATING THE PISTON IS ADJUSTED TO MAINTAIN THE PISTON IN PRESSURE BALANCE DURING THE EXTRUSION OPERATION. GRAVITATIONAL FORCES ACTING UPON THE PISTON CAUSE IT TO REST UPON THE UPPER SURFACE OF THE GELATINOUS MASS AND TO ADVANCE DOWNWARDLY THROUGH THE REACTOR AS THE GEL IS DISPLACED FROM THE CAHMBER. THE METHOD OF THIS INVENTION IS PARTICULARY SUITED FOR THE PREPARATION OF

June 5, 1973 A. M. SAREM 3,737,500

METHOD FOR EXTRUDING GELATINOUS MATERIAL Original Filed May 1968 6Sheets-Sheet 1 v, *3 Q 5k Q 85 "WE u q a Q 1 a nu; I

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lM/A M 54/75/44 June 5, 1973 A. M. SAREM 3,737,500

METHOD FOR EXTRUDING GELATINOUS MATERIAL Original Filed May 1968 6Sheets-Sheet 2 l NVENT OR.

AM/R M SIRE/l4 B QA- June 5, 1973 A. M. SAREM METHOD FOR EXTRUDINGGELATINOUS MATERIAL Original Filed May (5, 1968 6 Sheets-Sheet 5INVENTOR. 144/? M 514/9544 June 5, 1973 A. M. SAREM 3,737,500

METHOD FOR EXTRUDING GIELATINOUS MATERIAL 6 Sheets-Sheet 4 OriginalFiled May 6, 1968 444/)? M SAFE/14 avg), y

June 5, 1973 A. M. SAREM 3,737,500

METHOD FOR EXTRUDING GELATINOUS MATERIAL Original Filed May (3, 1968 6Sheets-Sheet 5 I NVEN TOR. 144/? M SIRE/14 June 5, 1973 A. M. SAREMMETHOD FOR EXTRUDING GELATINOUS MATERIAL 6 Sheets-Sheet 6 Original FiledMay 1968 Fza- 7 FIG- 6 INVENTOR. 444/? M 54/?544 United States Patent MUS. Cl. 264-142 3 Claims ABSTRACT OF THE DISCLOSURE A method forproducing particulated gelatinous substances, such as gelatinouspolymers, and solutions of these materials in which the gel is formed ina reaction chamber equipped with a hydraulically actuated piston andperforate extrusion head and the gelatinous product is subsequentlyextruded into a stream of solvent or nonsolvent liquid flowing atrelatively high velocity on the exterior of the perforate head. Thegelatinous substance is displaced from the reaction chamber byintroducing a fluid into the reaction chamber above the piston at asufficiently elevated pressure to displace the substance from thechamber through the perforate extrusion head. The hydraulic pressureactuating the piston is adjusted to maintain the piston in pressurebalance during the extrusion operation. Gravitational forces acting uponthe piston cause it to rest upon the upper surface of the gelatinousmass and to advance downwardly through the reactor as the gel isdisplaced from the chamber. The method of this invention is particularlysuited for the preparation of aqueous polymer solutions useful asflooding agents in the recovery of petroleum by water flooding, and isespecially adapted for installation at the site of a water injectionwell.

This is a division of application Ser. No. 726,840 filed May 6, 1968,and now issued as Pat. No. 3,558,759.

This invention relates to the particulation of gelatinous substances,and more particularly concerns a method for producing particulatedgelatinous polymers and polymer solutions. One specific embodiment ofthe invention involves a method for producing aqueous polymer floodingsolutions at the injection site which are useful in the recovery ofpetroleum by water flooding.

Various polymerization reactions and other processes are conducted thatyield gelatinous products which are desirably particulated prior todrying or other processing, or which are subsequently dissolved in asuitable solvent to yield a solution of the product. Heretofore,difficulty has been experienced in conveniently and economicallyparticulating or subdividing the gelatinous product for subsequentprocessing.

In another but related aspect, problems have been encountered inefliciently and economically producing polymer solutions useful in therecovery of petroleum by water flooding. It has been proposed toincrease the efiiciency and eifectiveness of a water flooding operationby employing as the flooding agent an aqueous media rendered moreviscous than ordinary water or brine by the incorporation therein ofwater-soluble agents, such as water-soluble organic polymers. Thesepolymers are generally produced as viscous liquid or gelatinous productsand subsequently dried to yield a solid product. The various polymerswhich have been suggested for use are largely available commercially inthe form of powders, solid granules and pellets, or in other finelydivided solid form. These solid polymers are generally difficult todissolve or disperse in water, often necessitating excessive mixing toobtain homogeneous solutions. Also, the resulting polymer solu- PatentedJune 5, 1973 tions prepared from the solid polymers must be strained orfiltered to remove undissolved solids that would cause plugging of theformation on injection. This is both wasteful of polymer andtime-consuming. Not only is additional processing cost involved inmanufacturing the particulated solid polymer and subsequentlyredissolving it in water or brine to provide the aqueous floodingsolution, but often the polymer also suifers some quality degradationduring dehydration and storage. Thus, need exists for a simple andeconomical process for producing aqueous polymer solutions useful in therecovery of petroleum by water flooding that can be practiced at thesite of the injection well, or in other field locations.

Accordingly, it is a principal object of this invention to provide animproved method for particulating a gelatinous material. Another objectof the invention is to provide an improved extrusion process forproducing a particulated gelatinous polymer. Another object is toprovide an improved method for producing polymer solutions. Stillanother object is to provide a method for producing an aqueous polymersolution at the site of the injection well that is useful as a floodingagent in the secondary recovery of petroleum. A still further object isto provide an improved extrusion process for particulating.

a gelatinous material. Other objects and advantages of the inventionwill be apparent from the following description.

Briefly, the present invention contemplates a method for producing bothparticulated gelatinous solids and solutions of the solid in which agelatinous material is formed in a reaction chamber equipped with ahydraulically actuated, vertically movable piston and a perforateextrusion head, and the gelatinous material is subsequently extrudedinto a stream of solvent or non-solvent liquid flowing at relativelyhigh velocity on the exterior of the perforate extrusion head. Thegelatinous material is displaced from the reaction chamber by a fluidmaintained under elevated pressure above the piston, the hydraulicpressure acting on the piston being adjusted to maintain the piston inpressure balance during the extrusion operation. Gravitational forcesacting on the piston cause it to rest upon the upper surface of thegelatinous mass and to advance downwardly through the reactor as the gelis displaced from the chamber. The gelatinous product is extrudedthrough the perforate extrusion head and into the liquid flowing on theexterior of the extrusion head, small pieces of the extruded gel beingsevered and carried away by the relatively high velocity liquid stream.These solid particles can be recovered from the liquid and dried, orthey can be subjected to further treatment. Alternatively, a solventliquid in which the particles of gelatinous extrudate dissolve to form asolution can be used to sever the extruded gel. One specific embodimentof the invention is particularly suited for the production of aqueouspolymer solutions useful as flooding agents in the recovery of petroleumby water flooding, and is adapted for practice in a field location suchas at the site of a water injection well.

The method of this invention is broadly useful for particulating anygelatinous substance, and is particularly useful in producing aparticulated gelatinous polymer. The term gelatinous substance as usedherein is inclusive of polymeric and nonpolymeric jelly-like semisolidsthat substantially retain their shape when unconfined, but which canreadily be conformed to the shape of their container. These materialscan range in consistency from extremely viscous liquids to substantiallysolid substances, and for purposes of this invention include allsubstances which can be extruded by the application of pressure andwhich tend to retain their shape when particulated.

In the practice of this invention to produce polymeric products, areactant monomer mixture, usually in the form of a solution of thereactant monomers, is charged to an extrusion reactor. A suitablecatalyst, such as a polymerization initiator or promoter, is admixedwith the reactant monomer solution, either as the solution is charged tothe reactor or after the solution is in the reactor. Once initiated, thepolymerization reaction is allowed to proceed to completion in aconventional manner, or until a desired degree of polymerization hasbeen attained, the resulting product of the reaction being a semisolid,gelatinous polymer. The polymer gel is extruded into a stream of solventor nonsolvent liquid flowing at relatively high velocity on the exteriorof the perforate extrusion head, small pieces of the extruded polymerbeing removed with the exiting fluid, and the particulated polymersubsequently being recovered from the liquid for further processing orbeing dissolved in the liquid to yield a solution of the polymer.

The invention will be more readily understood by reference to theaccompanying drawings, of which:

FIG. 1 is a schematic flow diagram of one embodiment of this inventionadapted for the production of particles of solid polymer;

FIG. 2 is a schematic flow diagram of another embodiment of thisinvention adapted for the production of polymer solutions useful asflooding agents in the secondary recovery of petroleum;

FIG. 3 is a front elevation view of the extrusion polymerization reactorof this invention;

FIG. 4 is a side elevation vieW of the extrusion reactor;

FIG. 5 is a top view of the extrusion reactor;

FIG. 6 is a cross-sectional view of the reaction vessel taken along theline 66 of FIG. 5;

FIG. 7 is an enlarged view of the perforate extrusion head; and

FIG. 8 is a diagram illustrating the forces due to pressure acting onthe piston during the extrusion operation.

One mode of practicing this invention to produce a particulated solidpolymer is illustrated in FIG. 1. A solution of reactant monomers, or amixture of monomers, is prepared in mixing vessel 10, which is equippedwith means for mixing its contents, i.e., such as the illustrated motordriven propeller mixer 12. The monomers and a suitable solvent arecharged to mixing vessel 10 in desired proportions and mixed to obtain asubstantially homogeneous solution of the monomers. Monomer solution iswithdrawn from vessel 10 through conduit 14 and transferred to extrusionreactor 30 by means of pump 16 and conduit 18. The polymerizationreaction is initiated by introducing a suitable catalyst or initiatorinto the monomer soluton, such as by transferring catalyst from catalystsupply means 22 through conduit 24 to reactor 30, as illustrated, or byintroducing the catalyst into the monomer solution passing throughconduit 18. Mixing vessel 10 and catalyst supply means 22 can beisolated from reactor 30 by valves 20 and 26 in conduits 18 and 24,respectively. Extrusion reactor 30 is generally comprised of a closedreaction vessel 32 equipped With a piston moved vertically through thevessel 32 by hydraulic drive unit 34. An extrusion head 36,constructedso that liquid can be circulated on the exterior of an internalperforate member through which the polymer is extruded, is located atone end of vessel 32. High pressure inert gas from high pressure gassource 46 is introduced into reaction vessel 32 through conduit 38 at arate controlled by valve 40. Gases can be vented from reaction vessel 32by means of conduit 42 and valve 44. A liquid in which the polymerparticles are substantially insoluble is circulated from separator 50 toextrusion head 36 by means of conduit 52, pump 54 and conduit 56. Liquidcarrying the suspended polymer particles is returned to separator 50through conduit 58. Solid polymer particles are separated from theliquid by screen 60 and recovered at 62.

In operation, a solution of monomers of the desired concentration isprepared in mixing vessel 10. With the piston retracted, monomersolution and catalyst are transferred to reaction vessel 32 or,alternatively, the catalyst is introduced into the monomer solutionpassing through conduit 18. If desired, air can be removed from thereaction vessel prior to charging the reactants by purging the vesselwith a substantially oxygen-free inert gas, by successively pressuringand depressurizing the vessel, or by drawing a vacuum in the vessel andthen breaking the vacuum with inert gas. After a desired degree ofpolymerization has been completed, liquid circulation is establishedfrom a separator 50 through extrusion head 36. The gelatinouspolymerization product is particulated by extrusion into the circulatingnonsolvent liquid passing through the extrusion head. Extrusion isaccomplished by introducing a fluid, i.e., a gas or a liquid, into thereaction vessel above the piston at a sufliciently elevated pressure todisplace the gelatinous polymer from the vessel through the perforateextrusion head. The hydraulic pressure actuating hydraulic drive unit 34is adjusted to maintain acpiston in pressure balance during theextrusion operation, as will be hereinafter more fully described, sothat the piston rests upon the upper surface of the gelatinous mass andadvances downwardly through the reaction chamber as the gel is displacedfrom the chamber because of the gravitational forces acting upon thepiston. The gelatinous polymeriztion product exits the reaction vesselthrough perforate extrusion head 36 and is sheared into small particlesby the liquid passing at relatively high velocity on the exterior of theperforate member. The liquid containing the particulate polymer isreturned to separator 50 and solid particles of the polymer recovered.The recovered polymer can be subjected to further processing steps, suchas Washing, drying, grinding, chemical treatment and the like, ifdesired, and the solid polymer particles can be segregated into suitablesize ranges. Alternatively, the liquid circulated through extrusion head36 can be a solvent for the extruded polymer and the polymeric productrecovered as a solution in this liquid.

Although the method of this invention can be employed to effect thepolymerization of many different monomers and mixtures of monomers, itis particularly useful in producing copolymers of acrylic acid andacrylamide, and terpolymers of acrylic acid, acrylamide and diacetoneacrylamide by the polymerization of the monomers in aqueous solution inthe presence of organoboron catalyst as described in US. Pat. No.3,476,186 and in copend-ing application Ser. No. 692,791, filed Dec. 22,1967, and now abandoned. The water-soluble acrylic acid-acrylamide andacrylic acid-acrylamide-diacetone acrylamide copolymers produced by thistechnique are especially useful as thickening agents for water or brineemployed in the recovery of petroleum from subterranean oil-bearingformations by water flooding.

The acrylic acid-acrylamide copolymer is prepared by copolymerizingacrylic acid and acrylamide in aqueous solution with an organoboroncatalyst. The acrylic acidacrylarnide-driacetone acrylamide terpolymeris prepared by including diacetone acrylamide monomer in the reactantmonomer solution. The resulting polymeric product is a viscous liquid orgel comprising a substantially linear Water-soluble copolymer having aminimum of cross-linking and possessing superior Water thickening andother desirable properties, these properties being to some extentcontrolled by the selection of monomer types, proportions and thereaction conditions.

The polymerization catalysts useful in initiating these polymerizationreactions are organoboron compounds and particularly organoboroncompounds having the fol lowing generalized formula:

BRa

wherein R R and R are alkyl radicals, and preferably are alkyl radicalshaving less than about four carbon atoms in the alkyl group. Thus, thepreferred catalysts boron, triethylboron, tripropylboron,tri(n-butyl)boron and tri(isobutyl)boron. Further, it is within thescope of this invention to employ a mixture of the foregoingtrialkylboron compounds as the catalytic polymerization agent. Also,various boronous anhydrides and boronites exhibit the requisitecatalytic properties.

While the exact mechanism of the organoboron initiated polymerizationreaction is not clearly understood, it is believed that the reaction isof the free radical type initiated by a peroxide formed by the reactionof organoboron with trace quantities of oxygen. The organoboron is alsobelieved to complex with the free radical at the end of the polymerchain in such a way that termination of the reaction becomes lesslikely, resulting in the formation of polymers having molecular weightshigher than would be produced in the absence of the organoboroncompound. Further, the organoboron catalyzed reaction may result in apolymer having a diiferent composition or a different distribution ofsubstituent groups along the polymer chain than would be obtained by theother methods of polymerization. Thus, while I do not desire to be heldto any particular theory of operation, it has nevertheless beendemonstrated that polymer compositions prepared by this technique aresuperior in many important properties to those prepared by otherpolymerization techniques.

Although the presence of trace quantities of oxygen are believednecessary to initiate the free radical polymerization reaction, thepresence of excess oxygen terminates the polymerization reactionprematurely, thus resulting in a lower molecular weight polymer product.While it is preferred that excess oxygen be removed prior to initiatingthe reaction, polymerization with organoborons may be successful eventhough a relatively large quantity of oxygen is initially present in thereaction mixture since most of the oxygen is consumed by reaction withthe organoboron to produce more highly oxidized boron compounds whichare not effective in providing free radicals. Thus, the amount of oxygenin contact with the reactant solution during the polymerization reactioncan be controlled to suitable levels by evacuating and purging thereaction vessel of air to remove excess undissolved oxygen from thesystem prior to initiating the polymerization reaction, the optimumcontent of oxygen dissolved in the reactant solution being a molarconcentration about equal to the molar concentration of the organoboroncompound present. Accordingly, it is preferred in most applications thatthe reactant monomer solution contain between about 15 and about 600ppm. of dissolved oxygen based on the monomer content of the solution.Excess dissolved oxygen can be removed from the reactant solution, ifdesired, by stripping with an oxygen-free gas. Conversely, in thosecases where the reaction mixture is totally devoid of the necessaryquantity of oxygen to initiate the free radical reaction, it is Withinthe scope of this invention to add oxygen to the reaction mixture.

The polymerization of the acrylic monomers usually can be initiated atroom temperature although some mild heating may be necessary in certainpolymerization reactions. These reactions are generally exothermicand'are accompanied by a release of heat causing an increase in reactanttemperature. While normal temperature increases can be accommodated withno particular problem, too high of a rate for the exothermicpolymerization reaction would cause a significant increase intemperature, especially, after the solution has thickened so that heatdissipation is impaired. With increased temperature, further increasesin polymerization rate result. This tendency toward run awaypolymerization is greater with a higher concentration of monomers insolution. Higher temperatures can also cause cross-linking of thepolymer resulting in the formation of polymers having reduced watersolubilities and other inferior properties. With most of the organoboroninitiated reactant systems, it is pre ferred that the reactiontemperature be controlled below about 65 C. Accordingly, it is preferredthat the concentration of monomers be controlled below the level thatwill cause a temperature increase of a magnitude that will result in runaway polymerization, and more particularly at temperatures below about65 C. In most applications, excessive temperatures are not encounteredat reactant concentrations below about 30 weight percent monomermixture. Further, the reaction mixture can be cooled to preventexcessive temperatures. Although the minimum amount of the organoboroncatal'yst required to initiate the reaction will depend somewhat on theoxygen content of the system, as hereinbefore disclosed, it hasnevertheless been found that polymerization of most systems can beinitiated at catalyst concentrations of 5-200 ppm. of boron based on theweight of monomers present. Since the molecular weights of variouscatalysts are different, catalyst additions are conveniently based 011boron content, it being understood that ditferent amounts of the variousorganoboron compounds must be employed to provide equivalent quantitiesof boron.

In one preferred mode of practicing this invention, aqueous solutions ofacrylic polymers, such as the aforementioned acrylic-acid-acrylamide andacrylic acid-acrylamide-diacetone acrylamide copolymers, can be preparedwhich are particularly useful as thickening agents for flood wateremployed in the recovery of petroleum by water flooding. In this mode ofpracticing the invention, an aqueous solution of the reactant monomersis prepared and charged to an extrusion reactor from which a majorportion of the oxygen has been removed. The polymerization reaction isinitiated by adding a small amount of organoboron catalyst to themonomer solution, either in the exrtusion reactor or as it is beingtransferred into the reactor. Once initiated, the polymerizationreaction is allowed to proceed to completion, or until a desired degreeof polymerization has been attained. The product of this reaction is asemisolid gelatinous polymer which is at least to a limited extentsoluble in water. The gelatinous polymer is extruded into a stream, ofaqueous liquid flowing at relatively high velocity on the exterior ofthe perforate extrusion head. Small pieces or particles of the extrudedpolymer are severed by the impinging liquid and carried to theneutralization vessel for reaction with a suitable base, such as sodiumhydroxide, to form a carboxylate. The relatively concentrated,neutralized polymer solution is then further diluted with aqueous liquidto yield a polymeric concentrate available for further use, such asaddition to the flood water injected into a subterranean petroleumreservoir.

This mode of producing aqueous solutions of acrylic polymers is furtherillustrated in FIG. 2. The reactant monomer solution is prepared incovered mixing vessel 100. A substantially oxygen-free inert gas havinga low solubility, such as nitrogen, helium, or the like, is bubbled intothe monomer solution through conduit 102 at a rate controlled by valve104. Conduit 102 can be fitted with a sparger or other device, notshown, that distributes the gas more uniformly through the liquid. Theinert gas bubbling through the liquid mixes the monomer solution, stripsoxygen from the solution to reduce its dissolved oxygen content, anddisplaces air from the mixing vessel. Alternatively, mixing vessel canbe provided with a mechanical mixer, such as a motor driven propeller orpaddle mixer. Monomer solution is withdrawn from vessel 100 throughconduit 106, which terminates adjacent to the bottom of the vessel andis fitted with a suitable inlet screen 108. This construction isemployed to avoid a bottom suction line which could become plugged withsolid monomer. Monomer solution Withdrawn from vessel 108 throughconduit 106 is transferred to extrusion reactor 160 by pump 110 andconduits 112 and 114. Relief valve 116 protects the pump and piping fromexcessive pressure. A small quantity of organoboron catalyst isintroduced by means of conduit 120 to the monomer solution flowing totheextrusion reactor, and these reactants mixed by passage through inlinemixer 122 located in conduit 114. Inline mixer 122 can be of the typedisclosed in my copending application Ser. No. 701,617, filed Jan. 30,1968, and now issued as Pat. No. 3,582,048, in which conduit 120 isconnected to a side nozzle of the mixer. Alternatively, catalyst can beinjected directly into the monomer solution in extrusion reactor 160.Mixing vessel 100 and the catalyst system can be isolated from theextrusion reactor by valves 124, 126 and 128 in conduits 112, 114 and120, respectively.

Many of the organoboron compounds useful in initiating polymerization ofacrylic monomers are spontaneously ignited on contact with air.Accordingly, care must be exercised in the handling and storage of thesematerials. Also, difliculty has been encountered in obtaining pumpingequipment capable of delivering the extremely low volume flow ratesencountered in injecting the organoboron catalyst into the reactantmixture. One embodiment of catalyst storage and injection equipment thatlargely overcomes these problems is schematically illus trated in FIG.2. This apparatus comprises a pair of small closed vessels 130 and 132that are provided with cooling coils 134 through which water can becirculated to prevent the liquid contents of the vessels from becomingoverheated. Vessel 130 is provided with level alarm 136 to indicate thatthe volume of catalyst is near depletion. Mineral oil or similar liquidis stored in a third vessel 138 that is open to the atmosphere throughvent 140. Mercury, or other high density immiscible liquid, is employedas a displacement fluid to displace catalyst from vessel 130, thuspreventing the oil soluble catalyst from contacting the mineral oil. Theliquid organoboron catalyst, or a solution of the catalyst in a suitablesolvent, is charged to vessel 130 through inlet connection 142 Withoutcontact With air. As the catalyst is introduced into vessel 130, mercuryis displaced to vessel 132 through conduit 144 and mineral oil isdisplaced from vessel 132 to vessel 138 through conduit 146 and bypassvalve 148. Valve 148 is closed at the completion of the fillingoperation. Catalyst is charged to the reaction system by pumping mineraloil from vessel 138 through conduits 150 and 146 to vessel 132. An equalvolume of mercury is displaced from vessel 132 to vessel 138 throughconduit 144, and a similar volume of catalyst is displaced from vessel130 through conduit 120. The volume of catalyst delivered is controlledby the volume of mineral oil pumped into vessel 132. As catalyst isdisplaced from vessel 130, the level of mercury in vessel 130 increasesuntil the electrically conductive mercury completes the alarm circuitenergizing alarm light 136, or other alarm or shutdown device.Sufficient mercury is contained in the system so that it is notcompletely displaced from vessel 132 when the volume of catalyst invessel 130 is depleted. With this embodiment of apparatus, only mineraloil must be pumped, thereby eliminating the handling of mercury orcatalyst in the pumping equipment.

The extremely low flow rates are achieved by transferring mineral oilfrom vessel 138 with a pair of small positive displacement pumps 152 and154 connected so that a small differential volume of liquid isdischarged into vessel 132. Pump 152 is connected so that it takessuction on vessel 138 through conduit 150 and discharges both into thesuction of pump 154 and into conduit 146, and pump 154 discharges intothe suction of pump 152. The system is protected from over pressure byrelief valve 118. Pump 152 is constructed with a slightly highervolumetric capacity, or is operated at a slightly higher speed, so thatonly the dilference in volume between the volumes pumped by pumps 152and 154 is discharged into conduit 146. One means of controlling the netvolume pumped is to employ two pumps having the same volumetriccapacity, and to operate the pumps at slightly different speeds. Thiscan be readily accomplished with a constant speed electric motor 156 bydriving the pumps through gear drive 158 in which each pump is driven bydrive gears having slightly different gear ratios. The net volume pumpedcan be controlled by employing a variable speed drive unit so that themaster drive speed can be varied to control the volumetric rate pumpedto the reaction system, with the proportional volume pumped by each pumpremaining in a ratio fixed by the respective gear ratios.

Extrusion reactor 160 is generally comprised of'a closed reaction vessel162 equipped with a piston that is moved longitudinally through thevessel by hydraulic drive unit 164. An extrusion head 166 that containsas internal perforate member through which polymer is extruded islocated at the end of reaction vessel 162. Extrusion head 166 isconstructed so that liquid can be circulated on the exterior surface ofthe perforate member to sever the extruded polymer and to carry thesevered polymer particles from the extrustion head. In this embodimentof the invention, a reservoir of water or other solvent liquid ismaintained in recirculation vessel 17 0. Liquid is withdrawn from vessel170 through conduit 172 and circulated through extrusion head 166 bymeans of pump 174 and conduit 1'76. Liquid and extruded polymer isreturned to vessel 170 through conduit 178. The polymer at leastpartially dissolves in the circulating liquid and, being more dense thanwater, tends to settle to the bottom of recirculation vessel 170.Accordingly, it is preferred that the recirculated liquid be withdrawnfrom vessel 170' at a point near the liquid surface. Conduit 172 isprovided at its inlet with screen to prevent recirculation ofundissolved polymer particles.

The piston can be longitudinally moved through vessel 162 to anyvertical position by hydraulic drive unit 164, which is also used tomaintain the piston in pressure balance during the extrusion operation.Hydraulic drive unit 164 is powered by a hydraulic system comprised ofhydraulic fluid reservoir 1'82, hydraulic pump 184, high pressureconduit 186 containing three-way valve 190, and low pressure conduit 192containing three-way valve 194. Hydraulic fluid is pumped from reservoir182 to one or the other ends of drive unit 164 depending on the settingof valve 190. Hydraulic fluid is returned to reservoir 182 from theopposite end of the drive unit through low pressure conduit 192. Thedirection of movement of the piston is controlled by positioningthree-way valves 190 and '194. The hydraulic fluid supplied to thehydraulic drive unit is maintained at a preset value by pressureregulator 1'88. Alternatively, hydraulic drive unit 164 can be driven byhigh pressure gas, thus eliminating the need for reservoir 182 and pump184.

Extrusion of the gelatinous polymer from reaction vessel 162 isaccomplished by introducing high pressure gas into the vessel at a pointabove the piston to maintain in the vessel a pressure elevatedsufliciently to displace the gelatinous polymer from the vessel throughthe perforate extrusion head. High pressure gas is supplied from highpressure gas supply 200 through conduit 202 containing valve 204 andpressure regulator 230. Regulator 230' maintains the pressure inreaction vessel 162 at a preset 'value during the extrusion operation.The hydraulic pressure actuating hydraulic drive unit 164 is adjusted tomaintain the piston in pressure balance during the extrusion operation,as will be hereinafter more fully described, so that the piston restsupon the upper surface of the gelatinous mass and, because of thegravitational forces acting upon the piston, it advances downwardlythrough the reaction chamber as the gel is displaced from the chamber.

Neutralization vessel 210 is an open mixing vessel,

equipped with mixing paddles 216 rotatably driven by electric motor 218.On completion of the extrusion operation, the polymer solution and anyundissolved polymer contained in recirculation vessel 170 aretransferred to neutralization vessel 210 through conduit 212 providedwith valve 214. The polymer solution can be conveniently pressured fromvessel :170 by mean of high pressure gas supplied from high pressure gassource 200* through conduit 206 at a rate controlled by valve 208.Caustic and additional water are added to the polymer solution in vessel210 and its contents mixed until the neutralization reaction is completeand the polymer solution substantially homogeneous. Thereafter, thepolymer solution is transferred from neutralization vessel 210 topolymer concentrate tank 220 by means of pump 222 and conduit 224.

Mixing vessel 100, extrusion reactor 160', recirculation vessel 170,neutralization vessel 210, and the pumps, catalyst injection andauxiliary equipment can be conveniently mounted on a skid to provide aportable unit adapted for easy movement to a field location.

The above described polymerization apparatus can be installed in a fieldlocation such as at the site of a water injection well or wells, andused to produce a water soluble thickening agent for flood water. In theembodiment illustrated in FIG. 2, injection well 240 penetrates theearth 242 and is completed in a subterranean oil-bearing strata inconventional manner. Well 240 is provided with a well head valve 244,such as a conventional Christmas tree assembly. Fresh water or brine istransferred from flood water source 246 through conduit 248 and injectedinto injection well 240 in conventional manner. Polymer concentrate iswithdrawn from polymer concentrate tank 220 by pump 250 and transferredthrough conduit 252 to conduit 248, at a rate controlled by valve 254,whereupon the polymer concentrate is introduced in a minor proportioninto the flood water injected into the well to form therein a diluteaqueous polymer solution useful as a flooding agent. Other conventionalmeans of admixing the polymer concentrate and the flood water to producea dilute aqueous polymer solution can be employed.

In a preferred method of producing a viscous aqueous flooding solution,aqueous monomer solution containing about 10 to 30 percent by weightacrylic monomer is prepared in mixing vessel 100. The monomer cancomprise a single reactive acrylic compound, or a mixture of reactiveacrylic monomers, such as a mixture containing about to 40 parts byweight acrylic acid and 60 to 95 parts by weight acrylamide, or amixture containing about 15 to 35 parts by weight acrylic acid, 45 to 80parts by weight acrylamide, and 2 to 15 parts by weight diactoneacrylamide. Substantially oxygen-free inert gas, such as nitrogen orhelium, is bubbled through the monomer solution in mixing vessel 100 tomix the solution, to reduce the dissolved oxygen content of thesolution, and to displace air from the vessel. Air is removed fromreaction vessel 162 by purging with substantially oxygen-free inert gasand, with the piston retracted, monomer solution is transferred to thereaction vessel. Organoboron catalyst is added to the monomer solutiontransferred to the reaction vessel to initiate the polymerizationreaction, and polymerization is allowed to proceed until a gelatinouspolymer of the desired molecular weight is obtained.

Upon completion of the polymerization reaction, water is charged to therecirculation vessel and recirculation established through the extrusionhead 166. Gas is introduced at the top of reaction vessel 162 at apressure elevated sufliciently to displace the polymer gel from thereaction vessel and the pressure of the hydraulic fluid supplied tohydraulic drive unit 164 adjusted to maintain the piston in pressurebalance, as will be more fully disclosed hereinafter. The extrusion rateis adjusted by varying the gas pressure, higher pressures causing anincrease in extrusion rate and lower pressures reducing the extrusionrate. The extrusion rate is preferably maintained below the rate atwhich extruded polymer cannot be carried out of the extrusion head bythe circulated liquid, and accumulates in the head causing plugging.Hydraulic pressure is adjusted to maintain it in a fixed ratio with thegas pressure.

Polymer extruded from the reaction vessel is severed from the extrusionhead by the relatively high velocity water stream flowing on theexterior of the perforate head. The polymer is at least partiallydissolved in the water, and the polymer solution and undissolved polymerparticles are returned to recirculation vessel 170. At the completion ofthe extrusion operation, the polymer solution and undissolved polymerparticles are transferred to neutralization vessel 210. A base,preferably a monovalent base, such as ammonium hydroxide, sodiumhydroxide, or potassium hydroxide, and additional water are added to thepolymer solution in vessel 210. Preferably, sufficient base is employedto neutralize the carboxylic acid groups of the polymer to carboxylatesand to increase the pH of the solution to a value of about 8 to 10. Thesolution is mixed until the polymer is substantially completelydissolved and a homogeneous solution produced. The solution is thentransferred to polymer concentrate tank 220 for storage until required.

The polymer concentrate produced in this manner can be employed as athickening agent for flood water used in the recovery of petroleum bywater flooding. Water or brine is injected into a subterranean petroleumreservoir through a water injection well in conventional manner. A smallamount of polymer concentrate is added to the flood water to producetherein a concentration of about 0.002 to 0.5 weight percent polymer.This small amount of olymer renders the flood water more viscous andimproves its effectiveness for oil displacement. Alternatively, thepolymer solution produced in the foregoing manner can be employed forother uses, such as flocculation, thickening, soil stabilization, andthe like.

The various vessels can be sized so that a substantially continuoussupply of polymer concentrate is available from the otherwise batchprocess, and to eliminate unnecessary steps. For example, mixing vesselcan have sufficient capacity to permit the mixing of enough monomersolution for several polymerization reactions, and polymer concentratetank 220 can be sized so that sufficient polymer concentrate isavailable for continuous withdrawal in the desired quantities. Extrusionreactor 162 must have sufficient capacity to meet this demand, or two ormore units employed to produce the polymer concentrate.

One embodiment of the extrusion polymerization reactor of this inventionis illustrated in FIGS. 3 through 7 of the drawings, wherein similarreference numerals refer to like parts in the several views. Theextrusion reactor is comprised of a reaction vessel, generallydesignated by reference numeral 300, which is supported in a verticalposition by a suitable frame. Extrusion head 302 is mounted at the lowerend of reaction vessel 300. Hydraulic power unit 304 actuates a pistonin reaction vessel 300 and is adapted to move the piston longitudinallythrough the vessel to any vertical position therewithin, and to apply aforce to the piston to maintain it in pressure balance during theextrusion operation.

Reaction vessel 300 is a closed pressure vessel comprised of anelongated cylindrical shell 310 having end flanges 312 and 314 attachedat either end by convenient means, such as by Welding. Shell 310 can beconveniently constructed from a section of pipe. End flange 312 isprovided with a circumferential groove 316 in its mating face adapted toreceive 0 ring gasket 318. End plate 320 mates with flange 312 toprovide a fluid tight closure. End flange 312 and end plate 320 eachhave a plurality of matching holes spaced substantially uniformly abouttheir peripheries adapted to receive bolts 322. Shell 310 is aperturedat 324 and fitted with connector 326 adapted to receive the reactantinlet conduit. Extrusion head 302 is comprised of outer cylindricalmember 330 having flange 332 attached thereto, as by welding. Flange 332is provided with circumferential groove 334 in its mating face adaptedto receive ring gasket 336. Cylindrical member 330 is closed at itslower end by end plate 338 which is fluid-tightly attached about itsperiphery to member 330, as by welding, to form a unitary outer housingfor the extrusion head. Bottom plate 338 is apertured at 340 and fittedwith outlet conduit 342 through which recirculated liquid and polymerexits the extrusion head. Flanges 314 and 332 each have a plurality ofmatching holes spaced substantially uniformly about their peripheries toaccommodate bolts 344 which fluid-tightly attach the extrusion head toflange 314 to form the bottom section of the reaction vessel.Cylindrical member 330 and flange 332 are drilled to provide foursubstantially equally spaced tangential holes 346 which are adapted toreceive liquid inlet conduits 348 that communicate with the interior ofthe extrusion head. Conduits 348 are connected to recirculated liquidsupply conduit 350 to provide means for introducing a solvent ornonsolvent liquid into the extrusion head. Flange 314 and shell 310 aredrilled at 352 to receive conduit 354 that is fitted with valve 356 toprovide means for sampling and venting the reaction vessel.

Perforate extrusion member 360 is a basket shaped member adapted toremovably fit Within the outer cylindrical member 330. As moreparticularly illustrated in FIG. 7, internal extrusion member 360 iscomprised of perforate cylindrical member 362 and imperforate circularbottom plate 364 attached about its periphery to cylindrical member 362.Cylindrical member 362 is provided with outwardly projecting lip 366having a peripheral groove 368 about its circumference adapted toreceive O ring gasket 370. This construction provides a fluid-tight sealbetween the interior of member 330 and the exterior of member 362 at lip366 and maintains the perforate extrusion member 360 in spacedrelationship within the member 330. Lugs 372 on the exterior of bottomplate 364 maintain member 360 in spaced relationship with bottom plate338. Thus, cylindrical perforate member 360 is fluid-tightly mounted inspaced relationship within the outer housing, a clearance of about 0.05inch being maintained between the exterior of member 362 and theinterior of member 330, with a somewhat larger clearance between thebottom members. Liquid is introduced tangentially into this annularspace through the conduits 348 and passes along the perforate face ofmember 362, through the space below member 360, and exits throughconduit 342. Cylindrical member 362 contains a plurality of perforations374 substantially uniformly disposed about its circumference.Perforations 374 are preferably drilled through member 362 andcountersunk from the exterior. The diameter of the porforations in partdetermines the size of polymer particles extruded and should be selectedto produce the desired particle size. Perforate extrusion member 360*can be easily replaced with a similar unit having different sizeapertures to accommodate the production of different size particles.

Hydraulic actuator 304 is a conventional double acting hydraulic powercylinder containing a piston that is moved longitudinally through thecylinder by regulation of the pressure of the fluid supplied to thecylinder. Hydraulic actuator 304 is mounted in a vertical position abovereaction vessel 300 so that movement of the piston within actuator 304imparts axial movement to piston rod 380. An aperture is provided at thecenter of top plate 320 and fitted with packing gland 382 to provide afluid-tight seal around the axially movable rod 380. End plate 320 isalso apertured at 396 to receive gas inlet conduit 398. Piston rod 380is threaded at 386 to receive piston 388 and nut 390. Piston 388 is aflat plate adapted to loosely fit within reaction vessel 300. Since theprimary purposes of the piston are to prevent channelling of theinjected displacement fluid through the polymer gel during extrusion andto prevent retention of substantial polymer gel on the vessel wall, theseal between piston 388 and the vessel wall is not fluid-tight. Whilethe piston can be formed from a single circular metal plate 388, it ispreferred that it also include one or more plastic plates 392, that areslightly larger in diameter than plate 388, and a metal backing plate394.

Since some of the materials handled in reaction vessel 300 may becorrosive, it is advisable to construct the parts exposed to thecorrosive environment of corrosion resistant materials, such asstainless steels, or to clad or otherwise line the vessel to protect itfrom corrosion. For example, in the illustrated apparatus, end plate 320and bottom flange 314 are provided with an overlay or cladding ofstainless steel at 400 and 402, respectively, on their interiorsurfaces. Shell 310 and other metal members exposed to the corrosiveenvironment can be constructed of corrosion resistant metals orotherwise lined to reduce corrosion.

Vessel 300 and hydraulic actuator 304 can be supported by a suitableframe which can comprise a pair of base channels 410 and 412 maintainedin spaced relationship by crossmember 414, and a pair of verticalchannels 416 and 418 maintained in spaced relationship by crossmembers420 and 422. Lateral support for the vertical members is provided by twopair of gusset plates 424. Hydraulic actuator 304 is attached to members420 and 422 by a pair of clamps 426. End plate 320 is rigidly supportedin a horizontal position from vertical channels 416 and 418 by a pair ofbrackets 428 that are welded to the end plate and bolted to therespective vertical members. Reaction vessel 300 is attached to andsuspended below rigidly mounted end plate 320.

Reaction vessel 300 can be lowered for cleaning and repair by removingbolts 322, or only the extrusion head can be lowered by removing bolts344. Lowering of either the extrusion head or the entire reaction vesselis facilitated by means of jack 430 that is mounted on crossmember 414and adapted to bear against a base comprised of cylindrical member 432attached to bottom plate 338 and enclosed at its bottom by plate 434.Cylindrical member 432 is cut out at 436 to accommodate conduit 342. Apair of guide tracks 440 located on the inside of each of the verticalsupport members and a corresponding pair of projecting lugs 442 weldedto flange 312 cooperate to maintain the reaction vessel in substantiallyvertical alignment as it is raised or lowered.

When reacting an initial batch of polymer, a solid plate is insertedbetween flanges 314 and 332 to prevent the reactant monomer solutionfrom entering the extrusion head. On completion of the reaction, theplate can be removed without spilling the gelatinous polymer. The plateneed be used on only the initial run following cleaning of the reactor,as otherwise, sufficient polymer gel remains within perforate member 360to prevent the monomer solution from entering the extrusion head andattendant piping.

Polymer gel is extruded from the reaction vessel by a fluid maintainedin the vessel at an elevated pressure. Although this fluid can be aliquid and particularly a substantially nonsolvent liquid, it ispreferred that extrusion be accomplished by injecting a gas into thevessel above the gelatinous mass. The use of inert gases, such asnitrogen and helium, are particularly preferred, The pressure of thehydraulic fluid supplied to the hydraulic actuator is adjusted tomaintain the piston in pressure balance so that it rests on the uppersurface of the gelatinous mass and moves downwardly through the vesselby the force of gravity as polymer is withdrawn from the vessel. It hasbeen found that extrusion of the polymer by the application of a majorportion of the force by the hydraulic actuator causes polymer to bypassaround the piston and to accumulate above the piston, thus precludingits extrusion. Avoidance of polymer bypassing would necessitate the useof a carefully machined cylinder and a sealed piston, thereby addingadditional cost and limiting the practical size of the extrusionreactor. Further, it has been found that extrusion by gas displacementalone, without the use of a balanced piston, is impractical as the gasquickly channels through the polymer mass leaving most of the polymerunextruded. However, extrusion can be effectively accomplished by agaseous atmosphere maintained at elevated pressure in the vessel if apiston is maintained at the polymer surface under conditions such thatthe forces acting on the piston due to pressure are balanced.

The pressure of the fluid introduced into the reaction vessel above thepolymer mass is adjusted to maintain extrusion at a desired rate. Theextrusion rate should not be so high as to cause polymer to accumulatein the extrusion head or to cause the outlet conduit to become pluggedwith polymer. The pressure of the hydraulic fluid is then adjusted tomaintain the pressure forces acting on the piston balanced during theextrusion operation. The amount of hydraulic pressure necessary tomaintain the piston balanced depends upon the relative sizes of thepistons.

The nature of the forces due to pressure acting upon the piston areillustrated in FIG. 8 wherein piston 500 represents the piston inextrusion reactor 502, piston 504 represents the piston in hydraulicactuator 506, and rod 508 represents the piston rod interconnectingthese two pistons. As illustrated in the drawing, if the gravitationalforces acting on the piston and friction are neglected, piston 500 is atequilibrium, or pressure balanced, when wherein F is the force exertedby the hydraulic pressure in hydraulic actuator 506, F is the forceexerted by the fluid pressure upon the upper surface of piston 500 andforce F is the force exerted by fluid pressure on the lower surface ofpiston 500. Since the force is equivalent to the product of the pressureand the surface area upon which it is acting. Equation 1 can beexpressed as wherein P is the pressure of the hydraulic fluid, A is thesurface area of piston 504, P is the pressure of the fluid above piston500, A is the area of the upper surface of piston 500, P is the pressureof the fluid below piston 500 and A is the area of the bottom surface ofpiston 500.

Since piston 500 is not sealed in extrusion reactor 502, the fluidsabove and below the piston are at the same pressure and P =P Equation 2can be rewritten as Accordingly, the ratio of the extrusion pressure inreactor 502 to the pressure of the hydraulic fluid supplied to hydraulicactuator 506 at equilibrium can be predicted from a consideration of thegeometry of the respective pistons. The forces acting on piston 500 areunbalanced by virtue of the fact that the top surface of piston 500 hasa smaller effective area due to the area occupied by shaft 608. Thus,suflicient force is exerted on piston 500 by the hydraulic actuator tomaintain piston 500 under balanced pressure. The pressure forces actingon piston 500 will be balanced under all conditions wherein the ratio ofextrusion pressure to hydraulic pressure is as defined in Equation 3,the force of gravity then being the only net force acting to move thepiston downwardly. While it is preferred that the piston be maintainedbalanced during the extrusion operation, satisfactory opera- 14 tion canbe obtained so long as the ratio of the pressure in the reaction vesselto that of the hydraulic fluids is no less than the ratio calculated inaccordance with Equation 3. Accordingly, the pressures should beadjusted so that the ratio of the pressure in the reactor to thehydraulic pressure is equal to or exceeds the calculated ratio.

The improved extrusion polymerization method of this invention isfurther demonstrated by the following examples which are presented byway of illustration, and are not intended as limiting the spirit andscope of the invention as defined by the appended claims.

EXAMPLE 1 An aqueous solution containing about 15 weight percent acrylicmonomers is prepared by dissolving acrylic monomers in the proportion ofabout 1 part by Weight acrylic acid and 2 parts by weight acrylamide inWater. This solution is charged to an extrusion reactor from whichoxygen has been removed by purging with a substantially oxygen-freeinert gas. The extrusion reactor is equipped with a hydraulicallyactuated piston and a perforate extrusion head in accordance with theapparatus of this invention. Polymerization is initiated by addingtriethylboron catalyst to the monomer solution in the extrusion reactorin an amount equivalent to 20 parts of boron per million parts ofmonomer. The polymerization reaction is allowed to proceed for 16 hoursbefore extrusion is started.

On completion of the polymerization reaction, isopropyl alcohol iscirculated across the face of the perforate extrusion head at relativelyhigh velocity and extrusion initiated by injecting nitrogen into thereactor above the polymer mass. A pressure of 60 p.s.i.g. is maintainedin the extrusion reactor during the extrusion operation and the pressureof the hydraulic fluid supplied to the hydraulic actuator is adjusted tobalance the pressure forces acting on the piston during extrusion.Polymer is extruded through the perforate extrusion head and into thestream of isopropyl alcohol flowing across the face of the extrusionhead. The extruded polymer is severed by the impinging liquid stream andthe severed polymer particles carried out of the extrusion head by theexiting liquid. The polymer is substantially insoluble in the isopropylalcohol and is recovered from the liquid to yield a particulated solidpolymer product.

EXAMPLE 2 An aqueous solution of a water soluble acrylicacidacrylamide-diacetone acrylamide copolymer useful as a thickeningagent for flood water is prepared in the apparatus of this inventionwhich is located at the site of the water injection well. In accordancewith the method of this invention, an aqueous solution containing about20 weight percent acrylic monomers is prepared in the mixing vessel bydissolving about 27 parts by weight acrylic acid, 63 parts by Weightacrylamide, and 10 parts by weight diacetone acrylamide in water. Thesolution is mixed and excess dissolved oxygen removed by bubblingsubstantially oxygen-free nitrogen gas through the solution. Thissolution is transferred to an extrusion reactor from which a majorportion of the oxygen has been excluded by purging with nitrogen. Asolution of t1i(nbutyl)boron dissolved in dioxane is added to themonomer solution transferred to the reactor in an amount equivalent toabout 50 parts of boron per million parts of monomer. Polymerization isallowed to proceed for about 24 hours.

On completion of the polymerization reaction, water circulation isestablished from the recirculation vessel, through the extrusion headand back to the recirculation vessel. Extrusion is initiated byinjecting nitrogen into the reactor above the piston so as to maintain apressure of 200 p.s.i.g. therein. The pressure forces acting on thepiston are balanced by adjusting the pressure of the hydraulic fluidsupplied to the hydraulic actuator to 40 p.s.i.g. Polymer is extrudedthrough the perforate extrusion head and into the stream of waterflowing across the face of the extrusion head. The extruded polymer issevered by the impinging liquid stream and at least a portion of thepolymer particles are dissolved. The polymer solution and undissolvedpolymer particles are accumulated in the recirculation vessel. Oncompletion of the extrusion operation, the polymer solution andundissolved polymer particles are transferred to the neutralizationvessel. Sodium hydroxide and additional water are added in an amountsuflicient to neutralize the substituent carboxylic acid groups and toadjust the pH of the polymer solution to a value of 8.8, and thesolution mixed until homogeneous.

The polymer concentrate produced in the foregoing manner is added to theflood water injected into the subterranean petroleum reservoir in anamount sufiicient to establish therein a concentration of 0.05 weightpercent. The dilute aqueous solution of acrylic acid-acrylamidediacetoneacrylamide copolymer is an effective flooding agent for the recovery ofpetroleum by water flooding.

Various embodiments and modifications of this invention have beendescribed in the foregoing specification, and further modifications willbe apparent to those skilled in the art. Such modifications are includedwithin the scope of this invention as defined by the following claims.

Having now described the invention, I claim:

1. A method for producing a gelatinous extrudate, which comprises:

forming a gelatinous material in a closed extrusion vessel having afirst piston therewithin adapted for movement longitudinally throughsaid vessel, said piston loosely fitting within said vessel so as toextend transversely substantially across the cross-section of the vesselexcepting for a small gap between the edge of the piston and the wall ofthe vessel, said vessel having an extrusion head containing a perforatemember through which the gelatinous product is extruded, said extrusionhead being constructed so that a liquid can be flowed across the face ofsaid perforate member exterior of said vessel, and said piston beingmoved to a position in said vessel remote from said extrusion headduring the formation of said gelatinous material;

thereafter flowing a liquid across the exterior face of said perforatemember at relatively high velocity; injecting a fluid into said vesselon the side of said first piston remote from said extrusion head toelevate the pressure in said vessel sufficiently to force saidgelatinous material through said perforate member and into said liquidflowing on the exterior of said perforate member whereby said extrudedgelatinoim material is severed by said liquid to form particles of saidgelatinous material, the pressure in said vessel being adjusted toextrude the gelatinous material at a desired rate;

adjusting the longitudinal position of said first piston in said vesselso that said piston is maintained at the surface of said gelatinousmaterial in said vessel during the extrusion operation, said pistonbeing moved longitudinally through the vessel by a hydraulic operatorcomprising a cylinder containing a second piston rigidly connected tosaid first piston and wherein the pressure of the hydraulic fluidactuating said second piston is controlled so that the ratio of thepressure in the vessel to the pressure of the hydraulic fluid is notless than a value calculated by the formula wherein P is the pressure ofthe hydraulic fluid, P is the pressure in said vessel, A is the surfacearea of the piston in the hydraulic operator, A is the area of the uppersurface of the piston in the vessel, and A is the area of the lowersurface of said piston; and

withdrawing said liquid containing particles of gelatinous material fromsaid extrusion head.

2. The method defined in claim 1 wherein the gelatinous material issubstantially insoluble in the liquid passed across the exterior face ofsaid perforate member, and solid particles of said gelatinous materialare recovered.

3. The method defined in claim 1 wherein the gelatinous material issoluble in said liquid passed across the exterior face of said perforatemember, and said gelatinous material is recovered as a solutiondissolved in said liquid.

References Cited UNITED STATES PATENTS 3,042,970 7/ 1962 Terenzi 264113,213,170 10/1955 Erdmenger et a1 264142 2,617,169 11/1952 Bodkin264-441 2,774,104 11/1956 Miller 264-142 2,077,898 4/1937 Rolfl' 222-3903,128,912 4/1964 Cash 222390 3,327,906 6/1967 Gomann 2223 89 ROBERT F.WHITE, Primary Examiner J. R. HALL, Assistant Examiner U.S. Cl. X.R.254-5

